R1:cb63a4bb6e8d

Improve messaging and documentation around surplus schemata

Summary: Fixes T6795. Fixes T6813. We can give more tailored instructions for surplus schemata than we currently do, and provide more information on resolving them.

Test Plan:
- Ran `storage adjust` with just surplus schemata (friendly warning).
- Ran `storage adjust` with surplus schemata and other serious errors (more severe error).
- Read document.

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley

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